"Remember U.K. civil registration is index’d by date of birth registration and never by date of the birth. Registration of birth (by law) has no connection whatsoever to date of chapel admission or established church christening (by personal choice) "
Whilst agreeing generally with that statement, I suggest that "by date of birth registration" should really be "by the sequence of the entries in the local Registers' Index" or similar, as I have never seen any Scottish, English or Welsh BMD SR Registrations that contains a calendar date in place of the Index data.
Effectively therefore, a birth registered say on the day of that birth, could be followed immediately in the register by one that had occurred almost six weeks earlier, having the effect that a birth on and registered on the 7th January 2001, could be followed in the register by one that occurred on 26th November 2000 but not registered until 7th January 2001.
Interesting effects when not only a different year; but depending on interpretation, a different century and a different millenium!